1. CSCD 433 Advanced Networks
Lecture 2
Network Review
Spring 2018
Reading: Chapter 1 1 1

2. Topics Network Topics Some Review from CSCD330 Applications
Common Services
Architecture
OSI Model
AS and Routing Review
Packet vs. Circuit Switching
Review concepts for Design Goals 2

3. Review Topics for Design
Useful to review topics we covered in CSCD330 with respect to their design
This course will be exploring how network components fit together to form a complex system
Where in this system can we increase efficiency, change design for the better, look at continuing trends for networks

4. Review
Most of you know or recall many of the things we learned in CSCD330
See how much you remember 4

5. Building Blocks of Networks Applications
Look at network applications we all use
Look at network services they need

6. Building Blocks of Networks Applications
Two main types of applications
1. Data transfer
Web pages
File transfer
2. Streaming Audio and Video
Real-time Audio and Video
Voice Over IP
Some have elements of both ….
Online games.
Network Design Issues
Where to put common network services

7. Common Services Network Applications
What we want is to have common set of network services
Otherwise ….
Each application needs to build its own network communications
Why is this bad?
Makes applications more complicated than necessary
Redundant to build communications into each application

8. Common Services Challenge
To provide useful set of services that gives choices to applications
Need to understand “design patterns” of network applications
What are some common needs of network applications?

9. Common Services File Transfer
Important use of networks from the beginning
Involves a client sending a request and a server responding with data or Peers providing file chunks
Video or Audio Streaming or Static Text/Image Transfer
Two general types of channels
Request/Reply channel
Message Stream channel

10. Common Services Reliability Networks can fail
Machines crash, network lines are cut, electrical interference, deliberate interference, hardware problems
Ideally, network design should incorporate error correction so network applications don't need to be aware of failures

11. Common Services Security Network applications need security
Question is … should every application do their own encryption and other security protocols or
Should security be a service offered
Network level
Application level

12. Common Services Shared Resources
- Need to accommodate each application
Fair use of network
Regulate or stop traffic if too much
Allow full network use when traffic is light
Possible priority for some applications

13. Network Architecture Layering and Protocols Abstraction
How does abstraction work in software?
Hides details behind an interface
Manages complexity
Provides an interface that can be manipulated by other components of the system
Hides details of how object is implemented

14. Network Architecture Challenge Abstractions in Networks Layers !!!!
Identify useful abstractions to
provide universal service and
Do it efficiently
Abstractions in Networks
How do networks do abstraction?
Layers !!!!

15. Layering
Start with services provided by the hardware, then add layers, each providing services to the layer just above it
Why is this an advantage for networks?
Decomposes complex problem
Makes pieces more manageable
More modular design
Easier to add a new service or to modify
functionality of a layer

16. Layering Example Example of protocol layering HTTP - Web Browsing
Uses services from TCP, reliable delivery
Uses services provided by IP, unique addressing
Uses services provided by Ethernet, ARP address mapping from IP to MAC address
How do we refer to this set of Protocols?
Network Stack 16

17. Network Architecture Abstract Objects within a Network Protocols
Each layer, protocols use encapsulation
Attach headers/trailers to packets
Instructions for Peer protocols on receiving end
Body of message - data

18. Network Architecture OSI Model
Original OSI model and
Its Current or Modern Form
Who can draw these models on the board?

19. Original OSI Model, 7 Layers
End System
Application
Ignore the two extra layers
Presentation
Session
Transport
What does each layer do?
Physical
Data link
Network

20. Original OSI Model Application-specific exchange of messages
End System
Application
Presentation
Routing, segmentation and reassembly, network-wide addressing
Reliable delivery, error recovery, congestion control
Session
Transport
Physical
Data link
Network
Addressing, medium access, error control
Voltage, bit duration, connector type, etc.

21. Source: “Introducing TCP/IP,” by FindTutorials.com
OSI and the TCP/IP Suite
Source: “Introducing TCP/IP,” by FindTutorials.com

22. Essential Characteristics of IP
What are they?
Connectionless
Each IP datagram is treated independently and may follow a different path
Best effort
No guarantees of timely delivery, ordering, or even delivery
Globally Unique 32-bit Addresses
Usually expressed in dot-decimal notation:
Each interface has its own IP address

23. Essential Characteristics of IP
Time to Live (TTL)‏
TTL = 1
TTL = 2
TTL = 0
IP datagram TTL=3‏
Error msg
IP datagram headers contain a TTL field
At each router, this field is decremented; if it reaches 0, datagram is discarded and an error message is generated
Original purpose was to prevent datagrams from endlessly circulating within the network

24. ICMP Internet Control Message Protocol (ICMP)‏
Used by hosts, routers and gateways to communicate network layer information to each other
Typically used for error reporting
Uses IP Delivery
ICMP messages are carried as IP payload
ICMP messages
Type and code - contain first 8 bytes of IP datagram that caused ICMP message to be generated
Many Common Utilities
Ping, and Traceroute
Implemented by ICMP messages

25. Autonomous Systems (AS’s)‏
What are they?
Autonomous system (AS) is unit of router policy
Either single network or group of networks controlled by a common network administrator
On behalf of a single administrative entity
Such as a university, a business enterprise, or a business division 25

26. Autonomous Systems (ASes)‏
The Internet: A Network of Networks
Protocols between AS's?
Protocols within AS?
Autonomous Systems (ASes)‏
Abilene
Comcast
Georgia
Tech
AT&T
Cogent
ISPs and Telephone Companies
Have their Networks, connected using routers that support communication in a hierarchy
Companies contract with each other for mutual use of backbone resources
Define protocols for communication between and within AS's 26

27. Network Trends and Open Problems
Making networks easier to manage
Has been strong interest in “self-managing” networks
Improving trust/identity in networks, security
Spam, phishing attacks, etc.
Policy-related issues (net neutrality, government censorship, spying on civilians)
Meeting increasing demands of diverse set of applications
Real-time needs, bandwidth consumptive
Streaming video, VOIP, Television over IP 27

28. Network Models 28

29. Network Communication Models
Recall, What are the two main ways networks communicate? Two types of models …
1. Circuit Switching
2. Packet Switching

30. Circuit Switching Resources are reserved
Establishes a connection (circuit) to the destination
Source sends data over circuit
Constant transmission rate
Example: Telephone Network
Very early versions: Human-mediated switches.
Early versions: End-to-end electrical connection
Today: Virtual circuits 30

31. Circuit Switching Advantages and Disadvantages? Advantages
Fast and simple data transfer, once circuit has been established
Predictable performance since circuit provides isolation from other users
Guaranteed bandwidth 31

32. Circuit Switching Advantages and Disadvantages? Disadvantages
Does not handle bursty traffic very well
Users have differing needs for bandwidth
What if all resources are allocated? 32

33. Packet Switching Resources are not reserved Packets are self-contained
Each has a destination address
Source may have to break up single message
Each packet travels independently to the destination host
Routers and switches use the address in the packet to determine how to forward the packets
Packet + address 33

34. Resource Sharing: Packet Switching
Statistical multiplexing
Switches Arbitrate between inputs
Can send from any input that’s ready
Links are never idle when traffic to send
Efficient
Requires buffering/queues 34

35. Forwarding: Packet-Switched Networks
Each packet contains a destination in the header
Much like a postal address on an envelope
Each hop (“router” or “switch”) inspects the destination address to determine the next hop 35

36. Summary Brief review of CSCD330 content Beginning of Network Design
Network applications - Common Services
- Their needs for network services
- How we can optimally meet these needs
More topics later … Stay Tuned

37. Next time: Reading Chapter 1 for this lecture, Chapter 2 for next time
End 37